[HL ch 9] Electrolysis of Concentrated Solutions

[n00l3]

In dilute solutions, I compare each ion's reduction/oxidation potential with H+ and OH- respectively.

However, for concentrated solutions, I keep reading that:

anode: Although salt anion may have lower oxidation potential than OH-, because it is more concentrated, it is discharged.

cathode: H+ is discharged.

Why is it that at the anode you consider the concentration of the ions, but at the cathode, I've only ever heard H+ is discharged in these situations? ;o What would be an IB way of thinking through this? ;3

Edited November 25, 2013 by n00l3

[TonyIntzi]

haha Dude, im taking a test on electrolysis on tuesday, and I have NO idea whats going on in this chapter.

[Dasza]

I'm not sure if this would help you in any way, but when I was preparing to the test in electrochemistry I did all questions from question bank and the only question in which they asked about it was:

"Deduce the equations for the formation of the major product at the positive electrode (anode) when the following aqueous solution are electrolysed:

(1) dilute sodium chloride

(2) concentrated sodium chloride "

And the answer is:

(1) A(+) 2 H₂O -> O₂ + 4H⁺ + 4e^-

(2) A(+) 2Cl^- -> Cl₂ + 2e^-

Also in one of my books it is written:

"On anode water is oxidised to oxygen gass unless the electrolyte contains easily oxidised anions, such as bromide and iodide ions, with E<1.23"

But this definition says nothing about the concentration.

It was probably not very helpful, as I don't know a right answer for this either, but in past IB papers a common appearing substance is NaCl, so it is probably good to at least remember how ions Cl^- are acting